ACT Fibernet — plan was changed by the company without my consent and I was charged a fee for the same

I was having ACT Rapid plus monthly plan.
On 18th Feb, the plan was changed automatically to a higher value Blaze 6months plans without any request from my side. At that time I was not at my home for 1 week.
When I noticed the same after coming back on 21st Feb, I requested for reversal of plan to ACT Rapid plus monthly which was done on 25th Feb.

Now the company is charging an amount for higher value blaze plan on prorated basis. I have raised request 6 times with the customer care and escalated the request multiple times but no one is willing to help.